The present invention generally relates to gas generation systems and particularly to systems and methods for nitrogen generation and for inerting aircraft fuel tanks.
Aircraft fuel tanks contain potentially combustible combinations of oxygen, fuel vapors, and ignition sources. The flash point for explosion varies according to temperature, pressure and fuel type. Industry literature suggests that a “limiting oxygen content” (LOC) immunizes a fuel tank from explosion, regardless of flash point factors. Industry standards suggest various limits for the LOC. For example, current standards suggest that the minimum amount of oxygen needed to sustain combustion at sea level is slightly less than 12%. That amount increases to 14.5% at 30,000 feet above sea level, Croft, John, “FAA ‘Breakthrough’: Onboard Inerting”, Aviation Week & Space Technology, Jan. 6, 2003.
Attempts have been made to reduce the oxygen level in aircraft fuel tanks by providing fuel tank foam systems to arrest explosions. Drawbacks exist, however, in foam inerting systems, including displacement of approximately 3.5% of the volume of the tank and inefficiencies associated with mandatory removal of the foam for maintenance purposes. Other inerting systems include a nitrogen-generating system (NGS), which introduces nitrogen enriched air into the fuel tanks. Typically, an NGS passes compressed air from the engines through filters to separate out the nitrogen content, which is then piped into aircraft fuel tanks.
For example, U.S. Pat. No. 6,360,730 B1 to Koethe claims a method for inert loading of jet fuel by directly injecting an inerting agent into jet fuel while it is being loaded onboard an aircraft. U.S. patent application Ser. No. 20020162915 A1 to Mitani claims an environmental unit for an airplane wherein air of high-temperature and high-pressure is extracted from an engine or an auxiliary power portion of an airplane. The extracted air is regulated in temperature and pressure by an air conditioning portion and then the regulated air is supplied to a pressurized chamber, where the air exhausted from the pressurized chamber or air drawn out of the pressurized chamber is separated into air enriched with nitrogen and air enriched with oxygen. The air enriched with oxygen is supplied to the pressurized chamber again. The air enriched with nitrogen is supplied to the fuel tanks. The air enriched with oxygen is once again supplied to the pressurized chamber by making use of the circulation line of the auxiliary air conditioning portion.
The prior art inerting systems, however, have drawbacks, including a requirement for costly operational components. The components monopolize a predominance of the space and weight allowances for an aircraft, impeding overall system design. Further, redundant processes such as repetitive airflows into and from air conditioner components result in operational inefficiencies, again increasing the overall costs of such systems.
As can be seen, there is a need for an improved method and system for gas generating systems and methods. There is also a need for such a system to and method to minimize component requirements; to minimize process complexity; to optimize safety features; and to minimize structural and operational costs.